Method of preparing secondary nitramines



United States Patent 3,410,905 METHOD OF PREPARING SECONDARY NITRAMINESMarvin H. Gold, Sacramento, and Milton B. Frankel,

Menlo Park, Calif., assignors to Aerojet-General Corporation, Azusa,Califi, a corporation of Ohio No Drawing. Original application June 26,1964, Ser. No. 378,456. Divided and this application Feb. 6, 1967, Ser.No. 630,481

6 Claims. (Cl. 260583) ABSTRACT OF THE DISCLOSURE This patent describesa novel method of preparing secondary nitramines of the formula whichcomprises reacting a dialkyl carbamyl halide of the formula with nitricacid at a temperature from about 30 C. to about C. wherein in the aboveformulae, R and R are lower alkyl and X is halogen.

This application is a divisional application of Ser. No. 378,456, filedJune 26, 1964, now abandoned.

This invention relates to a new and improved method for the preparationof secondary nitramines.

It is an object of the present invention to provide a novel process ofconverting secondary amines to secondary nitramines.

This and other objects of the present invention will become apparentfrom the more detailed description which follows.

We have discovered a new method for the preparation of aliphaticsecondary nitramines by treating a dialkyl carbamyl halide with nitricacid as shown in the following equation:

wherein in the above equation, R and R are lower alkyl radicals of fromabout 1 to 6 carbons, such as methyl, ethyl, propyl, sec-butyl,neopentyl and hexyl; and X is halogen, preferably chloride, bromine orfluorine.

The process of Reaction I makes possible the preparation of secondarynitramines from starting materials, all of which are readily availableon the commercial market. Our process of producing nitramines may becarried out in batch or by continuous operation. In either case, theprocess provides advantages which will come to be appreciated by thoseskilled in this art. Previously, the preparation of the nitraminescommonly involved treating a secondary amine with nitric acid, aceticanhydride and a halide catalyst such as hydrochloric acid, eithersimultaneously or sequentially. Inherent in this synthesis route is theevolution of substantial quantities of heat due to the exothermic natureof the reaction. The heat evolution makes it diflicult to control thereaction and to minimize the production of less desirable by-products.

In contrast thereto, by the present process the desired nitramines areproduced in a manner which is less exothermic and hence, readilycontrolled.

Reaction I is normally carried out at atmospheric pres- 3,410,905Patented Nov. 12, 1968 sure and, preferably, at a temperature of fromabout -30 C. to about +20 C. It should be understood that carrying outthe reaction under vacuum or elevated pressure is also contemplated. Theuse of an inert reaction solvent, such as trifluoroacetic anhydride,trifluoroacetic acid, or acetic anhydride is desirable. Alternatively,an excess of one of the reactants may serve as a solvent.

In the preferred process, nitric acid and trifluoroacetic anhydride arepreferably, although not necessarily, used in about equimolar amounts ora slight excess of nitric acid. The nitric acid employed in this mixtureis usually of the concentrated type, i.e., from percent to about 99percent by weight of HNO This nitrating mixture may be used in a widerange of proportions with respect to the dialkyl carbamyl halide.Generally an excess of the nitrating mixture is employed to obtain thehighest yields.

The products of Reaction I are ordinarily recovered by extraction,drying and/ or evaporation.

The following exampes illustrate the process of Reaction I.

Example I.Preparation of dimethyl nitramine To 91.7 ml. (0.663 mole) oftrifluoroacetic anhydride was added 30.8 ml. (0.733 mole) of 99 percentnitric acid, cooling being required to maintain the temperature at 5 to0. The solution was cooled to 30 and 14.7 grams (0.137 mole) ofdimethylcarbamyl chloride was added dropwise. The mixture was allowed towarm to 10 and the resulting solution was distilled at 2 mm. toapproximately half the volume and poured on grams of ice. The solutionwas basified with sodium hydroxide to a pH of 11 and treated with etherin a liquid extraction for 16 hours. After drying and evaporating theether phase, there was obtained 5.3 grams (43.1 percent) of faint yellowcrystals, M.P. 49 to 53. The product was sublimed at 40/2 mm. There wasno depression in melting point when mixed with an authentic sample ofdimethyl nitramine.

Example II.Preparation of diethyl nitramine To 91.7 ml. (0.663 mole) oftrifluoroacetic anhydride was added 30.8 ml. (0.733 mole) of 99 percentnitric acid, cooling being required to maintain the temperature at 5 to0. The solution was cooled to 30 and 0.13 mole of diethylcarbamylchloride was added dropwise. The mixture was allowed to Warm to 10 andthe resulting solution was distilled at 2 mm. to approximately half thevolume and poured on 150 grams of ice. The solution was basified withsodium hydroxide to a pH of 11 and treated with ether in a liquidextraction for 16 hours. After drying and evaporating the ether phase,there was obtained a 40.2% yield of crystalline produce, 11 1.4528. Theproduct was sublimed at 45/0.6 mm. There Was no depression in meltingpoint when mixed With an authentic sample of diethyl nitramine.

Example III.Preparation of diisopropyl nitramine To 0.6 mole oftrifluoroacetic anhydride is added 0.7 mole of 99 percent nitric acid,cooling being required to maintain the temperature at 5 to 0 C. Thesolution is cooled to 30 C., and 0.14 mole of diisopropylcarbamylchloride is added dropwise. The mixture was allowed to warm to 10 C. andthe resulting solution is distilled to approximately half the volume andpoured on 150 grams of ice. The solution is basified with sodiumhydroxide to a pH of 11 and treated with ether in a liquid extractionfor about 16 hours. After drying and evaporating the ether phase, thereis obtained a good yield of crystalline product. There is no depressionin melting point when mixed with an authentic sample of diisopropylnitramine.

Example IV.Preparation of dihexyl nitramine To 0.6 mole oftrifiuoroacetic anhydride is added 0.7 mole of 99 percent nitric acid,cooling being required to maintain the temperature at to 0 C. Thesolution is cooled to -30 C., and 0.15 mole of dihexylcarbamyl chlorideis added dropwise. The mixture is allowed to warm to C., and theresulting solution is distilled to approximately half the volume andpoured on 150 grams of ice. The solution is basified with sodiumhydroxide to a pH of 11 and treated with ether in a liquid extractionfor about 16 hours. After drying and evaporating the ether phase, thereis obtained a good yield of product. There is no depression in meltingpoint when mixed With an authentic sample of dihexyl nitramine.

By the process just described, other secondary amines can be convertedto nitramines. Thus, dibutylcarbamyl chloride can be converted todibutyl nitramine, dipentylcarbamyl bromide to dipentyl nitramine,ditertiarybutylcarbamyl bromide to ditertiarybutyl nitramine, anddiheptylcarbamyl chloride to diheptyl nitramine.

The nitramine compounds produced by this process are useful as highexplosives and can be used in any conventional explosive missile orprojectile as the main explosive charge. An example of such a missile isdisclosed in United States Patent No. 2,470,162, issued May 17, 1949.One way of using the high explosives of this invention in a device suchas that disclosed in United States Patent No. 2,470,162, is to pack thecrystalline explosive in powder form into the warhead of the missile. Acharge thus prepared is sufficiently insensitive to withstand the shockentailed in the ejection of a shell from a gun barrel under the pressuredeveloped from ignition of a propellant charge, and can be caused toexplode on operation of an impact or time fuse mechanism firing adetonating explosive.

Having fully described the invention, it is intended that it be limitedonly by the lawful scope of the appended claims.

We claim:

1. The method of preparing secondary nitramines of the formula:

which comprises reacting a dialkyl carbamyl halide of the formula:

N --X R! with nitric acid at a temperature of from about -30 C. to about+20 C., wherein in the above formulae, R and R are lower alkyl and X ishalogen.

2. The method of preparing secondary nitramines of the formula:

\NNO2 RI which comprises reacting a dialkyl carbamyl halide of theformula:

with nitric acid in trifluoracetic anhydride at a temperature of fromabout 30 C. to about +20 0., wherein in the above formulae, R and R arelower alkyl and X is halogen.

3. The method of preparing dimethyl nitramine which comprises reactingdimethylcarbamyl chloride with nitric acid in trifiuoracetic anhydrideat a temperature of from about 30 C. to about +20 C.

4. The method of preparing diethyl nitramine which comprises reactingdiethylcarbamyl chloride with nitric acid in trifiuoracetic anhydride ata temperature of from about -30 C. to about +20 C.

5. The method of preparing diisopropyl nitramine which comprisesreacting diisopropylcarbamyl chloride with nitric acid in trifluoraceticanhydride at a temperature of from about 30 C. to about +20 C.

6. The method of preparing dihexylpropyl nitramine which comprisesreacting dihexylcarbamyl chloride with nitric acid in trifluoraceticanhydride at a temperature of from about -30 C. to about +20 C.

References Cited UNITED STATES PATENTS 2,856,429 10/1958 Sauer 260583CHARLES B. PARKER, Primary Examiner.

R. L. RAYMOND, Assistant Examiner.

